After a wellbore has been drilled, the wellbore typically is cased by inserting lengths of steel pipe (“casing sections”) connected end-to-end into the wellbore. Threaded exterior rings called couplings or collars are typically used to connect adjacent ends of the casing sections at casing joints. The result is a “casing string” including casing sections and connecting collars that extends from the surface to a bottom of the wellbore. The casing string is then cemented in place to complete the casing operation. After a wellbore is cased, the casing is often perforated to provide access to one or more desired formations, e.g., to enable fluid from the formation(s) to enter the wellbore.
Hydraulic fracturing is an operating technique where a fracturing fluid, typically water with selected additives, is pumped into a completed well under high pressure. The high pressure fracturing fluid causes fractures to form and propagate within the surrounding geological formation, making it easier for formation fluids to reach the wellbore. During a fracturing treatment, sand or other high compression strength proppant is pumped into the fractured formation to keep the fractures open and provide a high permeability path for fluids to flow from the formation to the wellbore after releasing the treatment pressure. After fracturing is complete, the pressure is reduced, allowing most of the fracturing fluid to flow back into the well and to the surface. Some residual amount of the fracturing fluid may be expected to remain in the surrounding formation and perhaps flow back to the well over time as other fluids are produced from the formation.
During normal operations, the well produces a combination of fluids, typically including a desired hydrocarbon fluid (e.g., oil or gas) and water (i.e., “produced water”). The produced water can originate from multiple sources such as connate water from different formation layers, fracturing fluid, water injected from a remote well and/or steam injected from a remote well. These latter examples are typical of a steam or water flooding operation designed to force hydrocarbons to flow to the producing well.
With greater understanding of the downhole environment, operators are able to improve production of hydrocarbons. As an example, operators may increase the production of hydrocarbons by shutting off or deterring production from water zones. Alternatively, operators may decrease unwanted gas production by shutting off or deterring production from gas zones. There exists a need for improved systems or methods for analysis of downhole environments before or during production.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereof do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.